Wick assembly for self-regulated fluid management in a pumped two-phase heat transfer system

Abstract

A two-phase closed-loop heat transfer system comprises a capillary-type evaporator 10, a condenser 11 (preferably also of the capillary type), and a vapor conduit 17 through which heat-laden working fluid in vapor phase is driven adiabatically from the evaporator 10 to the condenser 11. The evaporator 10 comprises a plurality of tubes 12 connected in parallel. A helically threaded capillary channel 39 is formed on the cylindrical interior surface of each tube 12, and a wick assembly 33 is positioned longitudinally within each tube 12. Each wick assembly 33 comprises a high-permeability wick 36 within which are embedded a first tubule 34 and a second tubule 35. The first and second tubules 34 and 35 are of low permeability, and have one closed end and one open end. The open end of the first tubule 34 is connected to a feed line 16 through which liquid-phase working fluid is delivered into the first tubule 34. Liquid-phase working fluid seeps through the first tubule 34 into the surrounding wick 36, and migrates through the wick 36 to the capillary channel 39 with which the wick 36 is in contact. Liquid-phase working fluid in excess of an amount needed to keep the capillary channel 39 wetted seeps from the wick 36 into the interior of the second tubule 35. The open end of the second tubule 35 is connected to a return line 18.

I claim: 
     
       1. A closed-loop heat transfer system comprising: (a) an evaporator having a capillary channel on an interior heat-exchange surface thereof for distributing working fluid in liquid phase over said heat-exchange surface by capillary action;   (b) a condenser;   (c) a vapor conduit connecting said evaporator to said condenser, said vapor conduit enabling working fluid in vapor phase to pass from said evaporator into said condenser;   (d) a wick assembly disposed within said evaporator, said wick assembly enabling delivery of working fluid in liquid phase to said capillary channel on said interior heat-exchange surface of said evaporator for evaporation therefrom to vapor phase, said wick assembly also enabling withdrawal from said evaporator of working fluid in liquid phase in excess of an amount needed to keep said capillary channel continuously wetted within working fluid in liquid phase, said wick assembly comprising: (i) a wick of relatively high permeability with respect to working fluid in liquid phase;   (ii) a dual open-sided tubular structure that is substantially nonpermeable with respect to working fluid in liquid phase; and   (iii) a pair of elongate wall members that are of relatively low permeability with respect to working fluid in liquid phase; said dual tubular structure and said pair of wall members forming an assembly that defines a first duct and a second duct, with a dividing wall separating said first duct from said second duct; one end of said first duct being closed and another end of said first duct being open, the open end of said first duct communicating with said feed line; one end of said second duct being closed and another end of said second duct being open, the open end of said second duct communicating with said return line; a first one of said pair of wall members having a permeability such that liquid-phase working fluid delivered into said first duct from said feed line is able to seep therethrough from said first duct into said wick, a second one of said pair of wall members having a permeability such that liquid-phase working fluid in excess of said amount needed to keep said capillary channel continuously wetted with working fluid in liquid phase is able to seep therethrough from said wick into said second duct; said assembly formed by said dual tubular structure and pair of wall members being embedded in said wick, said dividing wall extending into said wick so as to prevent liquid-phase working fluid that seeps out of said first duct through said first one of said pair of wall members into said wick from passing directly to said second one of said pair of wall members for seepage into said second duct without first passing through a substantial portion of said wick; said wick assembly being disposed within said evaporator so that said wick is in contact with ridges defining a portion of said capillary channel on said interior heat-exchange surface of said evaporator, said substantial portion of said wick through which liquid-phase working fluid passes being adjacent said ridges, so that liquid-phase working fluid can be delivered from said substantial portion of said wick into said capillary channel by capillary action;     (e) a condensate line for withdrawal from said condenser of working fluid that has condensed from vapor phase to liquid phase in said condenser;   (f) a return line for withdrawal from said evaporator of working fluid in liquid phase in excess of said amount needed to keep said capillary channel continuously wetted with working fluid in liquid phase, said return line by-passing said condenser and merging with said condensate line;   (g) a pump, an inlet of said pump communicating with said condensate and return lines, said pump providing sufficient suction to withdraw from said condenser working fluid that has condensed to liquid phase therein, and to withdraw from said evaporator working fluid in liquid phase in excess of said amount needed to keep said capillary channel continuously wetted with working fluid in liquid phase; and   (h) a feed line connecting an outlet of said pump to said evaporator, said feed line delivering working fluid in liquid phase from said pump to said evaporator.   
     
     
       2. A closed-loop heat transfer system comprising: (a) an evaporator having a capillary channel on an interior heat-exchange surface thereof for distributing working fluid in liquid phase over said heat-exchange surface by capillary action;   (b) a condenser, said condenser comprising a tube having a helically threaded capillary channel on an interior heat-exchange surface thereof, said interior heat-exchange surface of said tube having an elongate groove thereon extending generally longitudinally with respect to said tube, said groove extending transversely with respect to said helically threaded capillary channel, said condenser further comprising a generally cylindrical elongate duct fixedly retained in said groove so that of an outer surface portion of said duct is in contact with ridges defining said helically threaded capillary channel, working fluid that condenses from vapor phase to liquid phase on said interior heat-exchange surface of said tube thereby being brought via said helically threaded capillary channel to said duct by capillary action, said duct having a permeability with respect to liquid-phase working fluid such that liquid-phase working fluid seeps into said duct from said capillary channel;   (c) a vapor conduit connecting said evaporator to said condenser, said vapor conduit enabling working fluid in vapor phase to pass from said evaporator into said condenser;   (d) a wick assembly disposed within said evaporator, said wick assembly enabling delivery of working fluid in liquid phase to said capillary channel on said interior heat-exchange surface of said evaporator for evaporation therefrom to vapor phase, said wick assembly also enabling withdrawal from said evaporator of working fluid in liquid phase in excess of an amount needed to keep said capillary channel continuously wetted with working fluid in liquid phase;   (e) a condensate line connected to said duct in said condenser for withdrawal from said condenser of working fluid that has condensed from vapor phase to liquid phase in said condenser;   (f) a return line for withdrawal from said evaporator of working fluid in liquid phase in excess of said amount needed to keep said capillary channel continuously wetted with working fluid in liquid phase, said return line by-passing said condenser and merging with said condensate line;   (g) a pump, an inlet of said pump communicating with said condensate and return lines, said pump providing sufficient suction to withdraw from said condenser working fluid that has condensed to liquid phase therein, and to withdraw from said evaporator working fluid in liquid phase in excess of said amount needed to keep said capillary channel continuously wetted with working fluid in liquid phase; and   (h) a feed line connecting an outlet of said pump to said evaporator, said feed line delivering working fluid in liquid phase from said pump to said evaporator.   
     
     
       3. A wick assembly to be positioned inside an evaporator tube having a capillary channel on an interior surface thereof, said wick assembly comprising: (a) a wick of relatively high permeability with respect to liquid-phase working fluid that is to be evaporated to vapor phase in said capillary channel;   (b) a dual open-sided tubular structure that is substantially nonpermeable with respect to working fluid in liquid phase; and   (c) first and second elongate wall members that are of relatively low permeability with respect to working fluid in liquid phase; said dual open-sided tubular structure and said first and second elongate wall members forming an assembly that defines a first duct and a second duct, with a dividing wall separating said first duct from said second duct; one end of said first duct being closed and another end of said first duct being open, the open end of said first duct being connectable to means for delivering working fluid in liquid phase into said first duct; one end of said second duct being closed and another end of said second duct being open, the open end of said second duct being connectable to means for withdrawing working fluid in liquid phase from said second duct; said first elongate wall member having a permeability such that liquid-phase working fluid delivered into said first duct can seep therethrough from said first duct into said wick, said second elongate wall member having a permeability such that liquid-phase working fluid can seep therethrough from said wick into said second duct; said assembly formed by said dual open-sided tubular structure and said first and second elongate wall members being embedded in said wick, said dividing wall extending into said wick so as to prevent liquid-phase working fluid that seeps out of said first duct through said first elongate wall member into said wick from passing directly to said second elongate wall member for seepage therethrough into said second duct without first passing through a substantial portion of said wick; said wick assembly being configured for positioning inside said evaporator tube transversely with respect to said capillary channel so that said wick is in contact with ridges defining a portion of said capillary channel, said substantial portion of said wick through which liquid-phase working fluid passes being adjacent said ridges, so that liquid-phase working fluid can pass by capillary action from said wick into said capillary channel.   
     
     
       4. A closed-loop heat transfer system comprising: (a) an evaporator having a capillary channel on an interior heat-exchange surface thereof for distributing working fluid in liquid phase over said heat-exchange surface by capillary action;   (b) a condenser having a capillary channel on an interior heat-exchange surface thereof;   (c) a vapor conduit connecting said evaporator to said condenser, said vapor conduit enabling working fluid in vapor phase to pass from said evaporator into said condenser;   (d) a wick assembly disposed within said evaporator, said wick assembly in said evaporator enabling delivery of working fluid in liquid phase to said capillary channel on said interior heat-exchange surface of said evaporator for evaporation therefrom to vapor phase, said wick assembly in said evaporator also enabling withdrawal from said evaporator of working fluid in liquid phase in excess of an amount needed to keep said capillary channel continuously wetted with working fluid in liquid phase;   (e) a wick assembly disposed within said condenser, said wick assembly in said condenser comprising an elongate porous structure extending through said condenser in contact with ridges defining said capillary channel on said interior heat-exchange surface of said condenser, working fluid that condenses from vapor phase to liquid phase on said interior heat-exchange surface of said condenser thereby being brought via said capillary channel to said porous structure by capillary action, said porous structure having a permeability with respect to liquid-phase working fluid such that liquid-phase working fluid seeps into said porous structure from said capillary channel;   (f) a condensate line connected to said porous structure of said wick assembly disposed within said condenser for withdrawal from said condenser of working fluid that has condensed from vapor phase to liquid-phase in said condenser;   (g) a return line for withdrawal from said evaporator of working fluid in liquid phase in excess of said amount needed to keep said capillary channel continuously wetted with working fluid in liquid phase, said return line by-passing said condenser and merging with said condensate line;   (h) a pump, an inlet of said pump communicating with said merging condensate and return lines, said pump providing sufficient suction to withdraw from said condenser working fluid that has condensed to liquid phase therein, and to withdraw from said evaporator working fluid in liquid phase in excess of said amount needed to keep said capillary channel continuously wetted with working fluid in liquid phase; and   (i) a feed line connecting an outlet of said pump to said evaporator, said feed line delivering working fluid in liquid phase from said pump to said evaporator.   
     
     
       5. The closed-loop heat transfer system of claim 4 wherein said porous structure of said wick assembly disposed within said condenser is made of material having a pore size that is sufficiently small to prevent any significant amount of working fluid in vapor phase from being drawn by said pump into said condensate line over a range of suction pressures, said range of suction pressures extending from a minimum pressure at which said excess working fluid in liquid phase seeps into said porous structure to a maximum pressure at which bubbles of working fluid in vapor phase start to be drawn into said porous structure.